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If you have the opportunity to build a network from scratch, and could design it such that the only devices to run routing protocols are routers, you could choose your favorite routing protocol and use that exclusively Typically, however, the situation is that there is an existing network with an existing routing protocol in place and, more often than not, Unix machines have some routing responsibilities in a network Because most Unix machines only support RIP, and it is unlikely that RIP will be the best choice of routing protocol for an internetwork of any size, the question arises of how more than one routing protocol can coexist on an internetwork, either permanently or during a period of migration The answer is redistribution A router can be configured to run more than one routing protocol and redistribute route information between the two protocols The idea is that the internetwork will have multiple domains, each operating with a different routing protocol At the border between these domains, one router has the responsibility of running both routing protocols and informing each domain about the other's networks in the appropriate routing protocol This is illustrated in Fig 423

The nice thing about wireless networks is the lack of cabling The wireless network requires only base backbone segments to connect the wireless cells to the wired network if there is one Once these are set up, the PC and network devices also need

1:

the special transmitter-receiver network interface cards to allow the PCs and devices to communicate with the cell and then through the cell to the servers Troubleshooting failed devices and cells is very easy and makes failed components easy to find and replace

.

In this figure, the router has to run both RIP and IGRP, then inform domain A about the networks in domain B with RIP updates and inform domain B about domain A's networks using IGRP updates The router in this figure will only be able to assign one metric to all the routes that it redistributes from one domain to another; it cannot translate metrics between protocols At first, this may seem to be a drawback, that all networks are redistributed with the same metric value, no matter where they are located in the other domain In reality this is not a problem, because to get from domain A to domain B, all connections have to go through the same router; the initial part of the journey is identical when sending packets between domains In Fig 4-23, a packet destined for domain A, originating in domain B, reaches router 1 Router 1 then has a routing table filled with entries for the networks in domain A that have been calculated using RIP updates The packet will follow the best path to its destination network The following is an example of how, in Fig 4-23, the routing protocol processes could be configured on router 1 to redistribute routes between the RIP and IGRP domains If we take a basic configuration for both RIP and IGRP, we add the redistribute commands shown in bold type: router igrp 12 timers basic 15 45 0 60 network 164800 network 193110

Disadvantages of wireless networks include a greater chance of signal interference, blockage, and interception Other devices and machinery that emit radio frequencies or noise can cause interference and static, which can disrupt the bubble of communication around the cell Another source of noise is lightning during storms This noise is the same static you hear when lightning strikes while you are speaking on a phone Blockage can occur in structures that are made of thick stone or metal, which do not allow radio frequencies to pass through easily This drawback usually can be overcome somewhat by changing the frequency used by the devices to a higher frequency You can determine early if this is going to be a problem in your building by trying to use a radio inside the building to pick up some radio stations If the radio will not pick them up, the building material is too thick to allow radio frequencies to pass through the walls This problem can be overcome by installing a cell in each room where a PC or network device will be placed Another major disadvantage with wireless is signal interception Signal interception means unwanted third parties could intercept wireless communications without physically being on the For the Network+ exam premises; they would simply have to be within you need to be able to visually recognize the signal range One of the key steps to securing the different network topologies from a wireless communication is to limit who can network diagram connect to the network and to encrypt the traffic in transit You will learn about wireless security in 7

There are two popular layouts for topologies: they are either point-to-point or pointto-multipoint A point-to-point topology also known as host to host is one system connected directly to another system In the past these systems would connect directly through the serial ports with a null modem cable, but these days, you could connect them using a crossover cable or a wireless connection

A point-to-multipoint topology uses a central device that connects all the devices together This topology is popular with wireless With point-to-multipoint, when the central device sends data, it is received by all devices connected to the central device But if one of the devices that are connected sends data, then it is received by only the destination system